Abstract Details

files Add files

epr2013_bsv.pdf2013-02-21 12:42:39Brian Victor

3d magnetic structure of HIT-SI plasmas at different injector driving frequencies

Author: Brian S. Victor
Requested Type: Consider for Invited
Submitted: 2012-12-07 15:34:51

Co-authors: T.R. Jarboe, B.A. Nelson, C.J. Hansen, A.C. Hossack, K.D. Morgan

Contact Info:
University of Washington
AERB Rm 120, Box 352250
Seattle, WA   98195

Abstract Text:
Current drive mechanisms at two different frequencies on HIT-SI are studied using bi-orthogonal decomposition. Recent modifications to the HIT-SI injector circuit were made to increase the injector driving frequency from 14.5 to 36.8 kHz. 36.8 kHz operations have achieved a current amplification of 3 with approximately 50% of the fueling rate of 14.5 kHz operations. Magnetic field profiles with injector operations at 36.8 kHz show an outward shift of the magnetic axis relative to 14.5 kHz operations. 187 surface and 46 internal magnetic probes are used to characterize the magnetic fields in HIT-SI. An m x n matrix is constructed with m the number of probes and n the time points of the signals. Using a technique known as bi-orthogonal decomposition (BOD) this matrix is decomposed into a set of orthogonal basis functions. An advantage of BOD over Fourier decomposition is the data are used to determine the basis set as opposed to imposing a basis set on the data. Analysis of the decomposition reveals that the first basis function corresponds to the spheromak equilibrium and the second and third basis functions to the injector fields. Further basis functions are investigated for their relation to magnetic field relaxation and current drive. For example, the oscillating amplitude of the fourth basis function shows a sharp change in frequency when the current ramp begins. Initially the oscillations are at the injector frequency and then, as the current begins to ramp up, the oscillation frequency doubles. This frequency doubling is consistent with the transition from reconnection driven to dynamo driven current drive.

Characterization: 1.4


University of Texas

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR2013)
February 12-15, 2013
Fort Worth, Texas

EPR 2013